1. Field of the Invention
This invention pertains to a wear-resistant tool insert for machines used in the production of nails, screws, rivets and similar objects starting with wire material.
2. Description of Related Art
Wear-resistant tool inserts of this type are employed in pairs in machines and are called impact or clamping jaws and pincer jaws. The clamping jaws are often used as inserts in toolholders. The inserts have elongated, prism-like trapezoidal cross-section base elements corresponding to similar recesses in the toolholders. One working surface of the clamping jaws has one or more clamping grooves for tightly clamping the supplied wire, and also a recess for forming the desired head shape of the object to be produced. The clamping jaws are arranged in the machine so that the clamping grooves are located opposite the paired inserts. In the course of the machine operation, the clamping jaws are closed or opened. In the closed state, the supplied wire is tightly clamped in the clamping grooves. In the clamped state, the head of the nail, screw or rivet is formed. For better clamping of the supplied wire, the clamping grooves are preferably transverse and semicircular in form.
After completion of the head, the part is elongated by closing two opposing pincer jaws. The pincer jaws are clamped tightly in toolholders or directly in the machine. They have a symmetrical profile with several cuts, through which, on the one hand, the end of the finished part is shaped and the part is elongated, and on the other at the same time, the initial geometry is created to shape the head of the next part.
A distinction is made, between single-wire and dual-wire clamping jaws, where either one or two clamping grooves are provided side by side.
The dual-wire form makes possible a simultaneous production of two nails, screws or rivets, that is, the production capacity is doubled. The pincer jaws are, as a rule, always of single-wire design, so that four pincer jaws are used in association with two-wire clamping jaws.
The tool inserts are often manufactured of hard metal to reduce wear. If the wear on the clamping grooves or on the cutters is excessive, then the inserts must be replaced.
Hard metal and other hard, wear-resistant materials indeed have a high compression strength and a very great hardness and thus a great wear resistance, but they can withstand only moderate tensile and bending loads. Based on irregularities in wire quality in connection with varying dimensions or different strengths in the manufacture of nails, screws, or rivets, very large tensile loads, and thus over stressing of the inserts of wear-resistant material may occur, which often is associated with fracturing of the inserts.